The grafting of ethylenically unsaturated monomers onto a molten polymer substrate with or without a free radical initiator is well known. For example, methods of grafting monomers such as maleic anhydride onto polyethylene in an extruder are described in U.S. Pat. Nos. 3,882,194 and 3,873,643.
In many applications, however, the monomer to be grafted is volatile and requires elaborate, complicated and often expensive apparatus and techniques to prevent escape of the volatile monomer from the polymer melt. Usually, the volatile monomer is both toxic and flammable, posing risks to personnel and equipment.
In addition, monomers such as acrylic acid, for example, are too reactive to be conveniently grafted to the polymer. Generally, such graft monomers will homopolymerize to an undesirable extent and not react with the polymer to be grafted to the desired extent.
Further, many monomers are not miscible or soluble in the polymer melt, resulting in poor dispersion of the monomer in the graft polymer product and considerable quantities of the monomer intended to be grafted being homopolymerized.
Further still, many monomers are liquid at room temperature and are consequently difficult to mix with a normally solid polymer substrate and too volatile to mix with a molten polymer substrate.